Electrical measuring instrument



Aug. 17, 1943., F. J. LINGEL ELECTRICAL MEASURING INSTRUMENT Filed Aug.11, 1941 mezzmar [/4622 Patented An 11, 1943 Frederick Joseph Lingel,Bluflton, Ohio,

. to The Triple Electrical Instrument Bluifton, Dhio, a corporation ofOhio assignor (20.,

Application August 11, 1941, serial No. 406,336 2 Claims. (01. 171-95)The present invention relates to electrical measuring devices andparticularly to meters such as an ohm meter for determining the ratiobetween two currents or two voltages, etc.

The primary object of the present invention is to provide an improvedmeasuring device for determining the ratio between two currents.

Another object is to provide an ohm meter in which the variations of theactuating electromotive force are utilized at the meter and do notaffect the indications of the instrument,

Still another object i to provide a current ratio meter employing twocoils, through which the respective currents are caused to flow, andsubjecting one of the coils to a magnetic fleld of constant value andthe other of the coils to a magnetic field of progressively increasingvalue as the current through that coil is increased.

The general object of the invention is to provide an improved meter forgiving an accurate direct reading of two or more current or voltagevalues in terms oi their ratios, notwithstanding variations in theelectromotive force which enersizes the instrument.

Figure 1 is an elevation, partly in section, of the preferred form of myinvention;

Figure 2 is a section on the line 2-2 of Figure 1;

Figure 3 is a section on the line 3-3 of Figure 1;

Figure 4 is a section on the line 4-4 of Figure 1;

Figure 5 is a diagrammatic view of the instrument connected in acircuit. I

The moving system of the usual type of DArsonval indicating electricalinstrument is caused to deflect under the influence of a torque exertedthereon by current-flowing through a coil suspended between the polefaces of a permanent magnet. The deflection is limited and the movingsystem comes to rest at a point where the restoring torque is equal andopposite to the deflecting torque. This restoring torque is usuallyapplied to the moving system through a spiral torsion spring, whichspring exerts a mechanical bias in direct proportion to the deflection.In many places where an electrical instrument of the indicating typecould be used,

I the power supply is not a constant voltage. Such application includesaircraft and automotive installation and many others where the source ofpower consists of a battery or generator. The voltage applied to theelectrical circuit in such a system is subject to numerous influencestending to cause it to vary. For instance, both the battery andgenerator voltages are functions of the rate at which they are supplyingpower. The battery voltage is further affected by the amount it has beendischarged. The generator voltage is also a function of its speed andwould vary with the speed of its prime mover.

The'above discussion as regards the introduction of errors by voltagefluctuation is also applicable to a moving vane type instrument in whichthe torque is exerted on the moving system by the interaction of amagnetic fleld set up in a coil by a current flowing through the same,and an iron vane rotatably suspended in the field of the coil. In thiscase, the vane may be either permanently magnetized or not. In either,case the net effect of a voltage fluctuation is to cause the magneticfield to fluctuate and the reaction of the vane thereon to fluctuate.The fluctuatinc: force exerted on the vane is opposed by a steadytorsional force from the spiral spring and the moving system is,therefore, not at rest. Any measuring device, therefore, based on thevoltage of a battery or generator balanced against the mechanical biasof a torsional spring will be in error by at least the same amount asthe voltage.

Referring now to the drawing in detail, and

in particular to Figures 1, 2, 3 and 4, the preferred form of myinvention is shown to be a DArsonval or moving coil type of directcurrent electrical instrument in which i designates a substantially Cshaped, laminated permanent magnet. Suspended between the opposedarcuate pole faces of the magnet l is the moving system of theinstrument and the soft iron cores about which the moving coils rotate.

The laminations of permanent magnet l are securely clamped togetherbetween shoulders l and nuts 3 of screws 2, as shown in Figure 1. Thescrews 2 also extend above the shoulders .c and terminate in studs,externally and internally threaded for the purpose of providingiurt'nersupport for other parts of the device. Secured between the shoulders &and nuts 5 are bridge 5 and formed plate I. The bridge 6 is apertured atthe center to adjustably receive a screw 8, the inner end of which is ajewelled bearing cup. The plate 7 is formed in such a manner that itengages the upper surface of the magnet, as at 9, and is securely heldin this position by the tabs Ill which are clamped between shoulders 4and nuts 5. By this means the depending portion ll of the plate I isrigidly held in axial alignment with the cores and moving coils and isuseful for supporting these parts.

The upper end of the upper core, designated I2, is supported by a narrowarm |3 extending inwardly from plate I. The lower end of core i2 and theupper end of the lower core, designated by numeral l4, are supported bya U shaped strip 5, riveted as at it, to the portion ll of plate 7.

The lower support of core I4 is likewise one arr'n of U shaped strip llriveted to H at Hi, the other arm extending across the bottom of themovement to receive the screw IS. The upper end of screw i9 terminatesin a jewelled cup, which, in conjunction with the jewelled cup in screw8, provides bearing points for the moving coil system. Rotatablysupported between the jewel bearings, in axial alignment with the cores2, I4, is the moving coil assembly comprising the two coils 2|], 2|separately wound onrectangular aluminum bobbins and cemented together orotherwise joined along 22 to form an integral unit. The supporting meansconsist of pivot shafts aflixed to the top and bottom of the coilassembly. The coils 20, 2| are so wound that the torques exerted by themon the moving system are in opposition, the torque due to currentthrough coil being the deflecting torque, and the torque due to 2| beingthe restoring torque, or vice versa. The aluminum bobbins on which thecoils are wound serve to damp the movements of the coil assembly andthereby prevent a too rapid deflection of the unit.

The upper pivot shaft is a portion of an assembly comprising, inaddition to the shaft, a pointer 23, counterweights 24, and a spiralfilament 25. The pointer is arranged to sweep over a dial 26 which ismounted on the internally threaded ends of screws 2 by screws 21. Thecounterweights are adjustable radially relative to the axis of themovement and serve to balance the moving system under all operating orrest conditions. The spiral filament is provided for the purpose ofconducting current into the coils 20 and 2| from the external circuitand is so constructed as to exert a minimum of torsional effect on themoving system.

The current is conducted from the external circuit into the spiralfilament through angle plate 28, which, for convenience in manufactureand assembly, is mounted about the screw 8. Plate 28 is held in positionby a spring washer bearing between the plate and the lock nut 29 onscrew 8.

The lower pivot shaft is a portion of an assembly comprising, inaddition to the shaft, two spiral filaments 3|] and 3| of the same lowtorsion character as filament 25. These filaments are provided for thepurpose of conducting current from the coils 20, 2| to the externalcircuit.

The filaments 30, 3| are connected at their inner ends to coils 2|, 20,respectively, and at their outer ends to angle plates 32, 33,respectively, and thence to the external circuit.

The inner ends of the twofilaments are mounted on the pivot shaft oninsulating collars and the angle plates 32, 33 are insulated fromeachother and the shaft by a nonconducting sleeve and nonconductingwashers. The sleeve (not shown) surrounds the screw l9 and the washers34 are placed so as to separate lock nut 35, plates 32, 33 and plate IT.The nut 35 serves at once to retain plates 32, 33 and to lock screw|9-in proper adjustment.

Referring now to Figures 1 and 3, it will be noted that the pole facessurrounding core I 2 and coil 20 are concentric with core i2. Coil 20requires.

coil 20 is therefore of unchanging value throughout the deflection ofthe instrument.

Referring next to Figures 1 and 4, it will be seen that the pole facessurrounding core i4 and coil M are eccentric to core i4. Coil 2| thenmoves in a nonuniform magnetic field. The restoring torque, due to acurrent flowing through coil 2| is therefore a function of thedeflection of the instrument, being the greatest when the deflectioncarries the movement to the extreme clockwise position, viewing themovement as in Figure 4. The exact shape of the pole faces surroundingcoil 2| and core i4 is not of consequence so long as the strength of thefield through which coil 2| moves is continually changing in the samesense. That is to say, that the eccentricity of the pole faces withrespect to the core M can be great or smallas the utility of theinstrument The effect of decreasing the eccentricity is to increase thesensitivity of the instrument, since the coil 2| must swing through agreater angle before balancing out any given increment of deflectingtorque exerted on coil 20. Obviously an increase in the eccentricity ofthe pole pieces would cause a corresponding decrease in the sensitivityof the meter. Further, the eccentricity of the pole faces need not be inthe form of a regular spiral, but can be irregular, in order to give alinear scale, if the change in field strength is always inthe samesense.

Referring now to Figure 5, the preferred form of my invention is shownconnected in a circuit which is representative of an aircraft orautomotive installation. In this figure, 40 is a storage battery of atype generally used in airplanes or automobiles. Battery 4|] isconnected through a current limiting resistor 4| into filament 25.Filament 25 is connected to coils 20, 2| by wires 62, 43, respectively.The opposite end of coil 20 is connected by wire 44 to the inner end offilament 3|. The outer end of filament 8| is connected by wire 45 to theparalleled resistors 46, 4!

and thence to the battery.

The other end of coil 2| is connected by a wire 48 to the inner end offilament 30. The outer end of filament 30 is connected by a wire 49 toresistor 50' and thence to the battery.

Resistor 4| is of relatively high value and is inserted in the circuitas a protective device to prevent excessive currents from flowingthroughthe coils 20, 2|,

Resistors 46 and 50 are calibrating resistors placed in the circuit tocontrol the sensitivity and response of the instrument.

Resistor 41 is the quantity being measured and in this case is shown asa bulb resistor placed in an engine block or crankcase for the purposeof perature of the body in which 41 is inserted.

Say that the resistor 41 is used to measure the temperature of the oilin an aircraft engine and assume that the temperature is now at thedesired point. The moving system of the instrument is then acted upon bya clockwise torque due to the current through coil 20 and acounterclockwise torque due to current through coil 2|. The movementwill then deflect clockwise until the constant deflecting torque of coil20 is balanced by the increasing restoring torque oi coil 2i. If now,the temperature of the oil in the crankcase increases, the resistance of41 will increase due to the rise in temperature the current through coil20 will decrease and the deflecting force will correspondingly decrease.The movement is now acted upon by unbalanced torques and will rotatecounterclockwise until the diminished deflecting force is balanced bythe diminishing restoring force. The movement therefore assumes a newposition of balance and a new reading is indicated on dial 26 by pointer23. If the temperature of the oil decreases, an opposite effect will beobtainedand the pointer will swing clockwise to a new position ofbalance.

If at any time during the operation of the instrument the voltage of thebattery 40 should vary it will be seen that the currents through thecoils 20, 2| will both vary in accordance with it. The net result ofthis will be to increase or decrease both torques by the same amount andcause no variation in the indication of the instrument.

The torsional effects of the spiral filaments 25, 30, 3| are negligiblein the normal operation of the instrument, but, should thebattery failor an open circuit result from a broken wire, the torque due to thespiral filaments will cause the pointer to swing counterclockwise offscale and thereby notify the observer of the fault. Thus, thisinstrument will measure and indicate the true value of the temperatureof a body being measured and will do so regardless of variation in thevoltage of the power supply.

It is obvious that this instrument would also be useful as an ohmrneterto measure the value of unknown resistances, as for instance in abattery powered portable ohmmeter.

It will be understood that I desire to comprehend within my inventionsuch modifications as come within the scope of the claims and theinvention.

Having thus fully described my invention, what I claim as new and desireto secure by Letters Patent, is:

l. A meter for determining the ratio between two currents, said metercomprising a pair of coils adapted to rotate between the poles of apermanent magnet, said currents being supplied to the coils inopposition, the pole face portions of the magnet adjacent one of saidcoils being eccentric to said one coil by a continuous increase in theair gap between the coil and each pole face in the same direction ofrotation of the coil, the pole face portions of the magnet adjacent theother of said coils being concentric to said coil.

2. A meter for determining the ratio between two currents, said, metercomprising a pair of coils adapted to rotate between the poles Of apermanent magnet, said currents being supplied .to the coils inopposition, said coils being secured together and mounted betweenbearings, torsionless spiral filaments connected between said bearingsand the coiis for supplying currents to the coils, the pole faceportions of the magnet adjacent one of said coils being eccentric to onesaid coil by a continuous increase in the air gap between the coil andeach pole face in the same direction of rotation of the coil, the poleface portions of the magnet adjacent the other of said coils beingconcentric to said coil.

FREDERICK JOSEPH LINGEL.

